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 $53.45   12.363%   $60.058   $60.06   $60.05   $60.10  
  Purchase #2 $169.41   13.140%   $191.6705   $191.67   $191.65   $191.70  
  Purchase #3 $226.76   7.376%   $243.4858   $243.49   $243.50   $243.50  
  Purchase #4 $218.98   7.715%   $235.8743   $235.87   $235.85   $235.90  
  Purchase #5 $111.61   4.637%   $116.7854   $116.79   $116.80   $116.80  
  Purchase #6 $151.25   7.736%   $162.9507   $162.95   $162.95   $163.00  
  Purchase #7 $109.76   13.139%   $124.1814   $124.18   $124.20   $124.20  
  7 purchase totals = $1,041.22       $1,135.0061   $1,135.01   $1,135.00   $1,135.20