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 $180.80   7.573%   $194.492   $194.49   $194.50   $194.50  
  Purchase #2 $185.93   9.162%   $202.9649   $202.96   $202.95   $203.00  
  Purchase #3 $31.72   11.237%   $35.2844   $35.28   $35.30   $35.30  
  Purchase #4 $220.25   7.641%   $237.0793   $237.08   $237.10   $237.10  
  Purchase #5 $103.30   12.336%   $116.0431   $116.04   $116.05   $116.00  
  Purchase #6 $147.61   4.791%   $154.682   $154.68   $154.70   $154.70  
  Purchase #7 $82.28   13.808%   $93.6412   $93.64   $93.65   $93.60  
  7 purchase totals = $951.89       $1,034.1869   $1,034.17   $1,034.25   $1,034.20