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 $179.88   7.570%   $193.4969   $193.50   $193.50   $193.50  
  Purchase #2 $203.50   11.802%   $227.5171   $227.52   $227.50   $227.50  
  Purchase #3 $32.77   9.221%   $35.7917   $35.79   $35.80   $35.80  
  Purchase #4 $57.74   8.693%   $62.7593   $62.76   $62.75   $62.80  
  Purchase #5 $163.40   3.442%   $169.0242   $169.02   $169.00   $169.00  
  Purchase #6 $241.65   7.531%   $259.8487   $259.85   $259.85   $259.80  
  Purchase #7 $200.89   13.740%   $228.4923   $228.49   $228.50   $228.50  
  7 purchase totals = $1,079.83       $1,176.9302   $1,176.93   $1,176.90   $1,176.90