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 $33.55   10.178%   $36.9647   $36.96   $36.95   $37.00  
  Purchase #2 $36.87   10.381%   $40.6975   $40.70   $40.70   $40.70  
  Purchase #3 $108.46   4.828%   $113.6964   $113.70   $113.70   $113.70  
  Purchase #4 $212.67   7.768%   $229.1902   $229.19   $229.20   $229.20  
  Purchase #5 $116.58   5.372%   $122.8427   $122.84   $122.85   $122.80  
  Purchase #6 $205.60   11.149%   $228.5223   $228.52   $228.50   $228.50  
  Purchase #7 $230.74   6.656%   $246.0981   $246.10   $246.10   $246.10  
  7 purchase totals = $944.47       $1,018.0119   $1,018.01   $1,018.00   $1,018.00