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 $151.53   11.542%   $169.0196   $169.02   $169.00   $169.00  
  Purchase #2 $54.37   13.270%   $61.5849   $61.58   $61.60   $61.60  
  Purchase #3 $113.50   9.672%   $124.4777   $124.48   $124.50   $124.50  
  Purchase #4 $140.27   5.436%   $147.8951   $147.90   $147.90   $147.90  
  Purchase #5 $203.29   6.424%   $216.3493   $216.35   $216.35   $216.30  
  Purchase #6 $120.70   8.527%   $130.9921   $130.99   $131.00   $131.00  
  Purchase #7 $93.53   3.645%   $96.9392   $96.94   $96.95   $96.90  
  7 purchase totals = $877.19       $947.2579   $947.26   $947.30   $947.20