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 $56.60   11.171%   $62.9228   $62.92   $62.90   $62.90  
  Purchase #2 $235.30   3.406%   $243.3143   $243.31   $243.30   $243.30  
  Purchase #3 $108.46   10.711%   $120.0772   $120.08   $120.10   $120.10  
  Purchase #4 $219.31   7.467%   $235.6859   $235.69   $235.70   $235.70  
  Purchase #5 $150.63   11.869%   $168.5083   $168.51   $168.50   $168.50  
  Purchase #6 $201.85   11.108%   $224.2715   $224.27   $224.25   $224.30  
  Purchase #7 $58.90   11.290%   $65.5498   $65.55   $65.55   $65.50  
  7 purchase totals = $1,031.05       $1,120.3298   $1,120.33   $1,120.30   $1,120.30