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 $231.53   13.703%   $263.2566   $263.26   $263.25   $263.30  
  Purchase #2 $95.74   7.135%   $102.571   $102.57   $102.55   $102.60  
  Purchase #3 $23.34   4.254%   $24.3329   $24.33   $24.35   $24.30  
  Purchase #4 $184.70   12.102%   $207.0524   $207.05   $207.05   $207.10  
  Purchase #5 $199.81   9.736%   $219.2635   $219.26   $219.25   $219.30  
  Purchase #6 $183.86   9.871%   $202.0088   $202.01   $202.00   $202.00  
  Purchase #7 $246.71   7.429%   $265.0381   $265.04   $265.05   $265.00  
  7 purchase totals = $1,165.69       $1,283.5233   $1,283.52   $1,283.50   $1,283.60