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 $148.26   10.672%   $164.0823   $164.08   $164.10   $164.10  
  Purchase #2 $187.45   3.839%   $194.6462   $194.65   $194.65   $194.60  
  Purchase #3 $207.52   9.485%   $227.2033   $227.20   $227.20   $227.20  
  Purchase #4 $233.74   5.368%   $246.2872   $246.29   $246.30   $246.30  
  Purchase #5 $54.88   8.860%   $59.7424   $59.74   $59.75   $59.70  
  Purchase #6 $8.72   5.142%   $9.1684   $9.17   $9.15   $9.20  
  Purchase #7 $124.98   10.655%   $138.2966   $138.30   $138.30   $138.30  
  7 purchase totals = $965.55       $1,039.4264   $1,039.43   $1,039.45   $1,039.40