Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $203.57   12.109%   $228.2203   $228.22   $228.20   $228.20  
  Purchase #2 $138.40   10.497%   $152.9278   $152.93   $152.95   $152.90  
  Purchase #3 $88.62   10.519%   $97.9419   $97.94   $97.95   $97.90  
  Purchase #4 $242.28   11.245%   $269.5244   $269.52   $269.50   $269.50  
  Purchase #5 $98.66   4.361%   $102.9626   $102.96   $102.95   $103.00  
  Purchase #6 $204.28   5.835%   $216.1997   $216.20   $216.20   $216.20  
  Purchase #7 $118.58   10.170%   $130.6396   $130.64   $130.65   $130.60  
  7 purchase totals = $1,094.39       $1,198.4163   $1,198.41   $1,198.40   $1,198.30