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 $168.27   11.146%   $187.0254   $187.03   $187.05   $187.00  
  Purchase #2 $31.30   6.389%   $33.2998   $33.30   $33.30   $33.30  
  Purchase #3 $226.74   8.485%   $245.9789   $245.98   $246.00   $246.00  
  Purchase #4 $92.40   12.450%   $103.9038   $103.90   $103.90   $103.90  
  Purchase #5 $69.65   8.261%   $75.4038   $75.40   $75.40   $75.40  
  Purchase #6 $201.40   9.210%   $219.9489   $219.95   $219.95   $219.90  
  Purchase #7 $181.52   9.628%   $198.9967   $199.00   $199.00   $199.00  
  7 purchase totals = $971.28       $1,064.5573   $1,064.56   $1,064.60   $1,064.50