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 $41.73   12.541%   $46.9634   $46.96   $46.95   $47.00  
  Purchase #2 $198.67   6.282%   $211.1504   $211.15   $211.15   $211.20  
  Purchase #3 $155.35   6.633%   $165.6544   $165.65   $165.65   $165.70  
  Purchase #4 $223.25   3.745%   $231.6107   $231.61   $231.60   $231.60  
  Purchase #5 $102.93   13.785%   $117.1189   $117.12   $117.10   $117.10  
  Purchase #6 $204.49   6.476%   $217.7328   $217.73   $217.75   $217.70  
  Purchase #7 $26.29   6.827%   $28.0848   $28.08   $28.10   $28.10  
  7 purchase totals = $952.71       $1,018.3154   $1,018.30   $1,018.30   $1,018.40