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 $85.39   7.702%   $91.9667   $91.97   $91.95   $92.00  
  Purchase #2 $135.54   7.457%   $145.6472   $145.65   $145.65   $145.60  
  Purchase #3 $24.25   11.347%   $27.0016   $27.00   $27.00   $27.00  
  Purchase #4 $41.97   7.261%   $45.0174   $45.02   $45.00   $45.00  
  Purchase #5 $211.84   11.764%   $236.7609   $236.76   $236.75   $236.80  
  Purchase #6 $230.87   12.433%   $259.5741   $259.57   $259.55   $259.60  
  Purchase #7 $162.64   10.667%   $179.9888   $179.99   $180.00   $180.00  
  7 purchase totals = $892.50       $985.9567   $985.96   $985.90   $986.00